1. Field of the Invention
This invention relates generally to implantable orthopedic prostheses and more particularly to instruments and surgical techniques for implanting orthopedic prostheses.
2. Background Art
Implantable orthopedic prostheses, in their most common form, comprise man-made replacements for the ends and articulating surfaces of the bones of the skeleton. Such prostheses are implanted to repair or reconstruct all or part of an articulating skeletal joint that is functioning abnormally due to disease, trauma, or congenital defect. Among the various articulating skeletal joints of the human body that are eligible to be fitted with implantable orthopedic prostheses, the hip joint and the knee joint are the ones most often treated with such prostheses. One reason for this is that the hip and knee joints are major weight bearing joints and degenerate more quickly than other joints in the event of abnormality. Another reason is that the hip and knee joints play a critical role in ambulation and quality of life, resulting in a greater demand for surgical correction of abnormalities.
With particular regard to the hip joint, the commonly employed orthopedic prostheses include components that fall within one of three principle categories: femoral stems, femoral heads and acetabular cups. A so-called xe2x80x9ctotalxe2x80x9d hip prosthesis includes components from each of those categories. The femoral stem replaces the proximal end of the femur and includes a distal stem that is received within the medullary canal at the proximal end of the femur. The femoral head replaces the natural head and articulating surface of the femur. The acetabular cup replaces the natural socket and articulating surface of the acetabulum of the pelvis. In some designs, the stem and head are an integral, unitary component, but more often the stem and head are separate modular components designed to be assembled together to suit the anatomical needs of the patient. In some other designs, including the so-called xe2x80x9cbipolarxe2x80x9d hip prostheses, only the femoral part of the hip joint is replaced and the artificial femoral head articulates directly against the natural acetabulum. In the case of the bipolar hip prosthesis, there is a second inner head that articulates within the outer head, hence the origin of the term xe2x80x9cbipolar.xe2x80x9d
Considering specifically the femoral stem component of implantable orthopedic prostheses, various configurations are available for use. The configuration that is most appropriate for a particular patient is often dictated by the condition of the bone of the proximal femur at the time the surgery is contemplated. Considered broadly, hip stems can be classified as either primary or revision stems, although some designs admit of use in either class. In general, primary hip stems are used for the first implantation in a particular femur, as they are the most bone-conserving by design. Likewise, the design of the primary stem is based on the assumption that the bone of the proximal femur is generally sound, except for the neck and the articulating surface of the head. Consequently, a primary stem may not be suitable where structurally critical bone of the proximal femur is unsound, or missing. Revision stems are designed for use in second and subsequent implantations in a particular femur, where there has been some loss of bone from prior surgery or from failure of a prior implant. In some patients, a revision stem would be the stem of choice for a first implantation where the bone of the proximal femur is unusually compromised.
One hip stem design, known as the calcar-replacing hip stem, typically employed as a revision stem, is particularly suited for use where the calcar femorale, a bony spur springing from the underside of the neck of the femur above and anterior to the lesser trochanter, is missing or compromised. The calcar femorale is important in providing structural strength to the proximal femur, and its absence contraindicates the use of a conventional primary or revision stem that depends on the calcar for support. The calcar-replacing hip stem includes a substantially horizontal flange designed to engage a horizontal proximal surface of the proximal femur that is created by resecting the femur below the natural location of the calcar femorale. Typically, the proximal femur is resected by two orthogonal planar osteotomies, one that is horizontal and extends from the medial side of the femur to about half-way to the lateral side, and one that is vertical and extends from the proximal extent of the femur down to the horizontal osteotomy. Consequently, a right-angular quadrant of the femur, including the neck and head, is resected. The calcar-replacing hip stem also includes a substantially vertical flange that engages the vertical resected surface of the proximal femur.
The current state of the art of fitting a calcar-replacing femoral stem prosthesis to a femur involves performing the horizontal and vertical osteotomies with a powered reciprocating saw blade, but in a freehand manner that depends for its success on the skill and technique of the implanting surgeon in making those osteotomies at the correct locations and in the proper planes. Any error in performing the osteotomies can result in the flanges of the calcar-replacing prosthesis not engaging the resected bony surfaces properly, or in the prosthesis being placed too low or too proud, or too lateral or too medial, with a consequent failure to restore the natural anatomic dimensions of the femur. It is desirable that the medullary canal be reamed to create a bony socket that closely conforms to the contour of the distal stem of the prosthesis. Ideally, when the prosthesis is inserted into the reamed medullary canal, the horizontal flange should engage the transversely resected horizontal bony surface approximately simultaneously with the distal stem becoming seated in engagement with the bony socket. Unless the relationship between the depth of the reamed socket and the location of the horizontal osteotomy is well-controlled, that ideal simultaneous engagement may not be achieved, resulting in the prosthesis-to-bone fit being less than optimum overall.
It would be desirable to provide an instrument system that provides for precise control and repeatability of the various reaming and osteotomy steps involved in implanting a calcar-replacing hip stem prosthesis to improve the ultimate fit of the prosthesis to the femur and to improve the outcome for the patient. Such desirable ends are achieved by the present invention, a preferred embodiment of which is described herein.
According to one aspect of the present invention, a trial prosthesis and saw guide instrument system is provided for use in orthopedic surgery to implant an orthopedic calcar-replacing femoral hip prosthesis. The instrument system comprises a trial femoral hip stem and trial flange, for temporary insertion at a resected proximal end of a femur within a reamed intramedulary canal of the femur. The trial femoral hip stem includes a longitudinal axis, a proximal portion and a distal portion, and a neck portion for temporarily receiving a trial femoral head. The proximal portion includes an elongate saw guide slot, substantially parallel to the longitudinal axis. The trial flange is configured for temporary insertion within the saw guide slot to simulate a vertical flange of a calcar-replacing femoral hip stem prosthesis.
According to another aspect of the present invention, an osteotomy guide and saw guide instrument system is provided for use in orthopedic surgery to implant an orthopedic calcar-replacing femoral hip prosthesis. The instrument system includes an elongate rotary reamer for reaming a socket in the medullary canal to receive the hip prosthesis, and an elongate driver adapter configured at a proximal end thereof for connection to a powered rotary driver and configured at a distal end thereof for connection to the elongate rotary reamer. An osteotomy guide has means for connection to the elongate driver adapter for rotary motion about the axis of the driver adapter, and includes a saw guide having a saw capture slot for capturing a saw blade therein to control the plane of cutting of the saw blade. The saw capture slot is oriented substantially perpendicular to the axis of the elongate driver adapter. Markings on the osteotomy guide, when aligned with the proximal extent of the greater trochanter, provide indication that the saw guide slot is disposed in the proper plane for guiding the transverse osteotomy. Means are provided on the osteotomy guide and driver adapter for controlling the axial position of the osteotomy guide relative to the driver adapter.
According to another aspect of the present invention, an osteotomy guide and saw guide instrument system is provided for use in orthopedic surgery to implant an orthopedic calcar-replacing femoral hip prosthesis. The instrument system includes a trial femoral hip stem for temporary insertion at a resected proximal end of a femur within a reamed intramedullary canal of the femur, and an elongate rotary reamer for reaming a socket in the medullary canal to receive the hip prosthesis. An elongate driver adapter has a proximal end configured for connection to a powered rotary driver and has a distal end configured for connection to the elongate rotary reamer. An osteotomy guide has means for connection to the elongate driver adapter for rotary motion about the axis of the driver adapter, and includes a saw guide surface for guiding a saw blade to control the plane of cutting of the saw blade. The saw guide surface is disposed in a plane substantially parallel to the axis of the elongate driver adapter and is offset medially from the axis by a distance sufficiently medial to prevent contact between the saw blade and the means for connection, and sufficiently lateral to guide a vertical osteotomy at a location where the spacing in the anterior-posterior direction between the inner cortical bone surfaces exceeds the spacing necessary to allow passage of the trial femoral hip stem therebetween.
It is an object of the present invention to provide surgical instrumentation that enables precise control and repeatability of various reaming and osteotomy steps involved in implanting a calcar-replacing hip stem prosthesis. Other objects and advantages of the present invention will be apparent from the following detailed description of a preferred embodiment, made with reference to the drawings.